Dude, the Dashain is next week. You can count "THIS" dashain in hours. So sorry to kill your excitment, but I don't think you can get her here for this Dashain. 

For next year, however, you should be able to. I am no asylee, so I don't know if there are any restrictions for their invitees. As long as you have GC, and you are not the one going over there, then should not be a problem. Others may shed more light on this. 

For the application, I don't think it's necessary to hire a consultancy. Are you planning to show some crooked documents? If not, the application process is very straightforward. It's done online and she can go for an interview with the supporting documents that makes the embassy believe that you can in fact sponsor her stay and/or she has enough ties that she will return back. That's it.